1. Field of the Invention
The present invention relates to injection molding machines, and, more particularly, to a die closing unit of an injection molding machine which includes a mounting arrangement for the interchangeable attachment to the die closing unit of injection units of different size.
2. Description of the Prior Art
Among die closing units for injection molding machines of the push-type, i.e. where the movable die half is pushed closed against the stationary die half, the most popular versions feature the use of a pair of parallel tie rods for the guidance of the movable die carrier plate and its attached movable die half. Besides serving as guide members, these stationary tie rods also serve as rigid frame members, linking the stationary die carrier plate on one end of the die closing unit to a stationary thrust plate, or a stationary cylinder head plate, on the other end of the die closing unit.
In most cases, the injection unit for such an injection molding machine also features two parallel tie rods which support and guide the injection unit. Where the injection unit is arranged for injection in the axial direction, through the stationary die carrier plate, the tie rods of the injection unit are preferably of the same diameter and axially aligned with the tie rods of the die closing unit. The extremities of both sets of tie rods are rigidly attached to the stationary die carrier plate, meaning that, while the tie rods of the die closing unit extend forwardly from the die carrier plate, the tie rods of the injection unit extend rearwardly from the same plate. The latter has appropriate seating bores and tie rod clamping means for this purpose.
Under certain circumstances, it becomes desirable to connect to the die closing unit an injection unit of a different size which may have tie rods which are spaced differently from the tie rods of the die closing unit. In the past, such a combination would require the use of a special adaptor unit which had a pair of forwardly extending short centering trunnions engaging the tie rod seats in the stationary die carrier plate and a pair of rearwardly facing tie rod seats having the special spacing required for the injection unit tie rods. Such a solution is disclosed in German Pat. No. 1 629 709. It implies the necessity of attaching to the stationary die carrier plate a comparatively heavy adaptor unit which, in order to provide the necessary stability, has to be of one piece, extending across the center axis of the unit, and having a large central opening for the injection cylinder. One shortcoming of this solution, apart from its cost, is the fact that the adaptor unit shifts the position of the entire injection unit rearwardly a considerable distance away from the die closing unit.